The best mappack to provide a challenge for experienced players is the NYS-5 series by Nyskrte. He says that completion rate is ~10%. Let's say this is true. We can't all make maps of the same quality, but we can aim to provide a challenge for the top 10% of experienced players who are looking for tests that are not solved in under five minutes. Only fair challenges, no glitches, exploits, bunny hopping or roller coasters.